Multidrug transporter over-expression is considered to limit access of antiepileptic drugs to the epileptic focus region and to be one cause of intractable epilepsy. To reach further proof for this multidrug transporter hypothesis, we compared P-glycoprotein expression rates in subgroups of Wistar rats which are sensitive or resistant to the anticonvulsant effect of the antiepileptic drug phenytoin in the amygdala-kindling model of temporal lobe epilepsy. In the electrode-implanted amygdala of phenytoin-resistant rats, the area labelled for P-glycoprotein was more than twice as large than that in phenytoin-sensitive rats. The data indicate that P-glycoprotein expression levels in the kindled focus have a critical impact on the anticonvulsant response to antiepileptic drugs.